dm thin metadata: add dm_thin_changed_this_transaction

Introduce dm_thin_changed_this_transaction to dm-thin-metadata to publish a
useful bit of information we're already tracking.  This will help dm thin
decide when to commit.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin-metadata.c

@@ -1375,10 +1375,9 @@ static int __insert(struct dm_thin_device *td, dm_block_t block,
 	if (r)
 		return r;
 
-	if (inserted) {
+	td->changed = 1;
+	if (inserted)
 		td->mapped_blocks++;
-		td->changed = 1;
-	}
 
 	return 0;
 }
@@ -1422,6 +1421,17 @@ int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block)
 	return r;
 }
 
+bool dm_thin_changed_this_transaction(struct dm_thin_device *td)
+{
+	int r;
+
+	down_read(&td->pmd->root_lock);
+	r = td->changed;
+	up_read(&td->pmd->root_lock);
+
+	return r;
+}
+
 int dm_pool_alloc_data_block(struct dm_pool_metadata *pmd, dm_block_t *result)
 {
 	int r;

drivers/md/dm-thin-metadata.h

@@ -148,6 +148,8 @@ int dm_thin_remove_block(struct dm_thin_device *td, dm_block_t block);
 /*
  * Queries.
  */
+bool dm_thin_changed_this_transaction(struct dm_thin_device *td);
+
 int dm_thin_get_highest_mapped_block(struct dm_thin_device *td,
 				     dm_block_t *highest_mapped);